The invention relates to a device for operating a gas exchange valve of an internal combustion engine with an electromagnetic actuator which includes an opening magnet and a closing magnet and an armature movably disposed between the opening and closing magnets for operating a valve shaft against the force of a closing spring.
Electromagnetic actuators for actuating gas exchange valves usually have two operating magnets, a valve opening magnet and a valve closing magnet, with opposite pole faces between which an armature is arranged. The armature acts directly or indirectly on a valve stem of the gas exchange valve. Actuators operating in accordance with the principle of mass-oscillation include a spring mechanism, wherein two springs act on the armature in opposite directions. Usually, two pre-stressed compression springs are used as the spring mechanism, of which one is a valve opening spring which biases the gas exchange valve in the valve opening direction and the other is a valve closing spring, which biases the gas exchange valve in the valve closing direction. When the magnets are not excited, the armature is retained by the valve springs in a position of equilibrium between the two magnets. This position corresponds to a center position, that is an equilibrium position of energy, between the two springs.
DE 35 13 107 C2 discloses a gas exchange valve with an actuator in which the armature, together with an opening spring, acts on the valve stem, via an armature tappet, against the force of a closing spring, which acts on the valve stem of the gas exchange valve.
DE 39 20 931 A1 discloses an electromagnetic actuator for gas exchange valves of displacement engines, in particular of internal combustion engines, which operates one or more gas exchange valves via a lever mechanism. The lever mechanism provides for a variable motion transmission between the actuator and the gas exchange valve. A play-compensating element compensates for the play, which is caused by the transmission system or which develops therein. The play-compensating element may be arranged in various positions in the transmission system either on the side of the gas exchange valve or on the side of the magnet, e.g. between the support structure of the lever system or between the closing magnet and the housing. The play compensation arrangement also includes a structure common to the gas exchange valve, or individual adjustment devices for changing the transmission ratios and to adapt the position of equilibrium of the oscillating system to the new spring forces by changing the position of one or more spring support points.
DE 39 20 976 A1 discloses a similar adjusting device in which a hydraulic play-compensating element is supported in the armature and engages the valve stem of the gas exchange valve. The play-compensating element may be supplied with oil under pressure via the armature. Also provided is a setting screw which is inserted in a top cover and acts on one support point of an opening spring which, with its other support point, engages the armature. By virtue of the setting screw, the position of equilibrium of the armature is adjustable such that the armature rests in the center between the operating magnets when the magnets are de-energized.
When the internal combustion engine is at a standstill, the hydraulic play-compensating element empties whereby the pre-determined position of equilibrium is changed in the direction toward the opening magnet. When the internal combustion engine is then started up again, the closing magnet has to generate a relatively high force. This causes a high mechanical, electrical and thermal load. Furthermore, in the closed position of the armature, there is a relatively large gap between the play-compensating element and the valve stem, which results in an annoying noise. In many cases, oscillation excitation of the system is not possible.
It is the object of the invention, to improve the start-up capabilities of an internal combustion engine controlled via electromagnetic actuators.
In a device for operating a gas exchange valve of an internal combustion engine having an electromagnetic actuator including an opening magnet and a closing magnet, between which there is arranged an armature which, together with an opening spring, engages a valve stem against the force of a closing spring, and a hydraulic play-compensating element arranged in the valve operating force transmission structure, the play-compensating element is installed in the transmission structure together with a mechanical adjusting element providing for minimal valve play when the engine is shut down.
The mechanical play compensating element compensates for all deviations or tolerances resulting from the manufacture so that the hydraulic play-compensating element need only compensate for the changes in length resulting from the operation of the internal combustion engine. As a result, any gap between the play-compensating element and the adjacent component is minimal when the engine is started up again after stand-still, with the result that no significant noise or excessive mechanical, electrical or thermal loading is generated. Operation of the internal combustion engine is possible however also with a defective mechanical play-compensating element.
The adjusting element may simply comprise an adjusting disc, an eccentric shaft or a setting screw. It may be arranged at various locations of the device, so that there is a high level of design freedom.
Further embodiments and advantages of the invention will become apparent from the following description of the invention on the basis of the accompanying drawings.